This may be a problem with DDE and Firefox tries to open the link via DDE, but also via the direct way (command line).
Try to redo the default browser setting and temporarily set another browser like IE as the default browser to force to recreate involved registry keys.
*http://kb.mozillazine.org/Default_browser
*https://support.mozilla.org/kb/How+to+make+Firefox+the+default+browser